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O'Donnell MJ, Fletcher M, Haley CA: KCl reabsorption by the lower malpighian tubule of rhodnius prolixus: inhibition by Cl (-) channel blockers and acetazolamide. J Insect Physiol. 1997 Jul;43(7):657-665.
Iono- and osmoregulation by the blood-feeding hemipteran Rhodnius prolixus involves co-ordinated actions of the upper and lower Malpighian tubules. The upper tubule secretes ions (Na (+), K (+), Cl (-)) and water, whereas the lower tubule reabsorbs K (+) and Cl (-) but not water. The extent of KCl reabsorption by the lower tubule in vitro was monitored by ion-selective microelectrode measurement of Cl (-) and/or K (+) concentration in droplets of fluid secreted by Malpighian tubules isolated under oil. An earlier study proposed that K (+) reabsorption involves an omeprazole-sensitive apical K (+)/H (+) ATPase and Ba (2+)-sensitive basolateral K (+) channels. This paper examines the effects acetazolamide and of compounds that inhibit chloride channels, Cl (-)/HCO (3)(-) exchangers and Na (+)/K (+)/2Cl (-) or K (+)/Cl (-) co-transporters. The results suggest that Cl (-) reabsorption is inhibited by acetazolamide and by Cl (-) channel blockers, including diphenylamine-2-carboxylate (DPC) and 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB), but not by compounds that block Na (+)/K (+)/Cl (-) and K (+)/Cl (-) co-transporters. Measurements of transepithelial potential and basolateral membrane potential during changes in bathing saline chloride concentration indicate the presence of DPC- and NPPB-sensitive chloride channels in the basolateral membrane. A working hypothesis of ion movements during KCl reabsorption proposes that Cl (-) moves from lumen to cell through a stilbene-insensitive Cl (-)/HCO (3)(-) exchanger and then exits the cell through basolateral Cl (-) channels. |
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